So after somewhat of a haphazard repair where i exchanged the mostfets Q1..Q4 with the incorrect replacements(wrong packaging), around 6 hours of listening later there was a noise in the speakers and silence after that. I tried turning the amp off and waiting a while but nothing. Tried exchanging the tubes as well, still no sound. The amp was idling for an extended period of time (~3 hours) and i was plugging and unplugging headphones (with the volume turned all the way down) when it happened.
So my suspicion is that my mosfets failed in a manner which took the high voltage bridge down with them. These are my voltage measurements, all taken with tubes installed.
1, 2: 0.116, 0.150
3, 4: 0, 0
5, 6: -1, -1
7, 8: -1, -1
9, 10: -1, -1
11, 12: 1, 1
13, 14: -9, -9
15, 16: 0, 0
17, 18: 0, 0
19, 20: 0, 0
21, 22: 0, 0
23, 24: 0, 0
25: 0
26: -31.5
27: -33.8
28: 6.1
29: 6.4
I also measured on the AC side of the HV bridge and i have ~280 or thereabouts VAC, 0VDC on the DC side of that bridge.
Plan now is to order correct mosfet replacements and some new bridges, but wanted to ask if you have any other recommendations for parts which likely let out the magic smoke such as zeners or resistors in the protection circuit? Will check as good as i can visually and with my DMM before i order parts.
So my suspicion is that my mosfets failed in a manner which took the high voltage bridge down with them. These are my voltage measurements, all taken with tubes installed.
1, 2: 0.116, 0.150
3, 4: 0, 0
5, 6: -1, -1
7, 8: -1, -1
9, 10: -1, -1
11, 12: 1, 1
13, 14: -9, -9
15, 16: 0, 0
17, 18: 0, 0
19, 20: 0, 0
21, 22: 0, 0
23, 24: 0, 0
25: 0
26: -31.5
27: -33.8
28: 6.1
29: 6.4
I also measured on the AC side of the HV bridge and i have ~280 or thereabouts VAC, 0VDC on the DC side of that bridge.
Plan now is to order correct mosfet replacements and some new bridges, but wanted to ask if you have any other recommendations for parts which likely let out the magic smoke such as zeners or resistors in the protection circuit? Will check as good as i can visually and with my DMM before i order parts.
So i've managed to source the correct FETs, exchanged them all, also swapped the broken bridge. There is a tiny amount of distorted sound in the right channel only, with the stock tubes.
These are my measurements with no tubes fitted:
Should i re-do the measurements with the tubes fitted? Still find it strange that the voltage at 19 and 20 are so far off, makes me suspect there's more damage to the stabilization circuit than just the Mosfets. What you reckon, swap the zeners in that circuit?
These are my measurements with no tubes fitted:
1,2 0, 0
3,4 0, 0
5,6 120, 119
7,8 121, 119
9,10 121, 119
11,12 1.1, 1.1
13,14 -9. -9
15,16 196, 194
17,18 0, 0
19,20 162, 160
21,22 162, 161
23,24 162, 161
25 319
26 -31
27 -33
28 7.6
29 7.6
3,4 0, 0
5,6 120, 119
7,8 121, 119
9,10 121, 119
11,12 1.1, 1.1
13,14 -9. -9
15,16 196, 194
17,18 0, 0
19,20 162, 160
21,22 162, 161
23,24 162, 161
25 319
26 -31
27 -33
28 7.6
29 7.6
Should i re-do the measurements with the tubes fitted? Still find it strange that the voltage at 19 and 20 are so far off, makes me suspect there's more damage to the stabilization circuit than just the Mosfets. What you reckon, swap the zeners in that circuit?